Subterranean reservoirs are commonly used to store fuels such as gasoline. Such fuel reservoirs are typically accessed through a fill pipe that leads from the ground surface to the fuel reservoir. Generally, the inlet to these fill pipes are recessed into pavement. Very common examples of this type of fuel reservoir are the gasoline fuel reservoirs used in automobile service stations.
Removable caps have long been used to seal the inlet of fill pipes. Such removable caps prevent fumes from escaping from the reservoir and keep the contents of the reservoir free from contaminants while allowing easy access to the reservoir for filling or servicing. Because these caps are fume-tight and the reservoirs are not always vented, pressure buildup sometimes occurs for a variety of reasons. For example, the volatile nature of many fuels, such as gasoline, readily change phase from liquid to vapor resulting in vapor pressure. This effect can be aggravated when the fuel reservoir is heated, as for example, when the sun radiates the paved surface over a fuel reservoir. Pressure buildup in fuel reservoirs can also occur due to vapor recovery systems used during the fuel dispensing process. Such vapor recovery systems force the recovered fumes back into the fuel reservoirs thus escalating the reservoir pressure. Whatever the source, the aggregate result is that fuel reservoirs can become highly pressurized.
While a highly pressurized fuel reservoir can cause problems when an operator removes the cap to access the reservoir, a sealed reservoir capable of containing high pressure is desirable when the tank is not being accessed. As is evident to one skilled in the art, pressurized fuel vapors contain significant amount of potential chemical energy. In a pressurized environment, portions of those vapors will diffuse back into the liquid fuel thus partially recovering potential chemical energy. In addition, a reservoir capable of containing high pressures will also prevent environmental pollution that may result is fuel vapors are released into the atmosphere. Therefore, fill pipe caps must have the capability of sealing high pressures within the fuel reservoir.
Caps for fill pipes must also satisfy a variety of other design constraints. For example, caps for fill pipes should be rugged enough to survive rough handling or outright abuse by operators. Additionally, caps for fill pipes should have a sufficiently low profile to fit within the recessed cavity between the inlet of the fill pipe and the surface of the pavement. A further design constraint is that caps for fill pipes should have the ability to lock and prevent unauthorized access to the fuel reservoir. Still other design constraints are apparent to one skilled in the art.
Thus, there is a need for a cap to seal the end of a fill pipe connected to a pressurized fuel reservoir, which eliminates the attendant problems.